Enhanced long-term attenuation of 1,4-dioxane in bioaugmented flow-through aquifer columns

Biologically active filtration (BAF) for metabolic 1,4-dioxane removal from contaminated groundwater

1,4-Dioxane is a persistent contaminant that is not effectively removed by conventional water treatment processes. In this study, bench-scale granular activated carbon (GAC)-based biologically active filtration (BAF) systems were developed to metabolically degrade 1,4-dioxane at environmentally relevant levels (<1000 μg L-1). BAF was established using predeveloped biologically activated carbon particles by mixing a 1,4-dioxane-degrading microbial community with granular activated carbon. 1,4-Dioxane removal performance was examined at a range of 1,4-dioxane concentrations (100-1000 μg L-1), hydraulic loading rates (3.6-14 cm h-1), and with the presence of co-contaminants (natural organic matter (NOM) and 1,1-DCE). BAFs achieved 69 ± 7 % removal with an influent 1,4-dioxane concentration of 100 μg L-1 and hydraulic loading rates of 3.6-14 cm h-1, with the lowest effluent concentration of 21 μg L-1. The presence of NOM and 1,1-DCE negatively and irreversibly impacted 1,4-dioxane removal performance of BAF, and pretreatment processes to remove co-contaminants are crucial to maintain the 1,4-dioxane removal efficiency. Microbial analysis revealed the enrichment of 1,4-dioxane degrading species (CB1190-like bacteria) and functional genes responsible for 1,4-dioxane biodegradation (dxmB and aldh) at the top 12 cm of the columns, suggesting the effectiveness of biological 1,4-dioxane removal within short column lengths. This study demonstrated effective metabolic 1,4-dioxane removal at environmentally relevant concentrations by the BAFs, and can provide insights into designing better 1,4-dioxane remediation strategies.

Delignified porous wood as biofilm support for 1,4-dioxane-degrading bacterial consortium

Delignified porous wood samples were used as carriers for biofilm formation of a bacterial consortium with the ability to degrade 1,4-dioxane (DX). The delignification treatment of the natural wood resulted in higher porosity, formation of macropores, increase in surface roughness and hydrophilicity of the treated wood pieces. These superior properties of two types of treated carriers (respectively, A and B) compared to the untreated wood resulted in 2.19 ± 0.52- and 2.66 ± 0.23-fold higher growth of biofilm. Moreover, analysis of the fatty acid profiles indicated an increase in proportion of the saturated fatty acids during the biofilm formation, characterising an enhancement in rigidity and hydrophobicity of the biofilms. DX initial concentration of 100 mg/L was completely degraded (detection limit 0.01 mg/L) in 24 and 32 h using the treated A and B woods, while only 25.84 ± 5.95% was removed after 32 h using the untreated wood. However, fitting the DX biodegradation data to the Monod model showed a lower maximum specific growth rate for biofilm (0.0276 ± 0.0018 1/h) versus planktonic (0.0382 ± 0.0024 1/h), because of gradual accumulation of inactive cells in the biofilm. Findings of this study can contribute to the knowledge of biofilm formation regarding the physical/chemical properties of biofilm carriers and be helpful to the ongoing research on bioremediation of DX.

1,4-Dioxane removal in nitrifying sand filters treating domestic wastewater: Influence of water matrix and microbial inhibitors

1,4-Dioxane is a recalcitrant pollutant in water and is ineffectively removed during conventional water and wastewater treatment processes. In this study, we demonstrate the application of nitrifying sand filters to remove 1,4-dioxane from domestic wastewater without the need for bioaugmentation or biostimulation. The sand columns were able to remove 61 ± 10% of 1,4-dioxane on average (initial concentration: 50 μg/L) from wastewater, outperforming conventional wastewater treatment approaches. Microbial analysis revealed the presence of 1,4-dioxane degrading functional genes (dxmB, phe, mmox, and prmA) to support biodegradation being the dominant degradation pathway. Adding antibiotics (sulfamethoxazole and ciprofloxacin), that temporarily inhibited the nitrification process during the dosing period, showed a minor effect in 1,4-dioxane removal (6-8% decline, p < 0.05), suggesting solid resilience of the 1,4-dioxane-degrading microbial community in the columns. Columns amended with sodium azide significantly (p < 0.05) depressed 1,4-dioxane removal in the early stage of dosing but followed by a gradual increase of the removal over time to >80%, presumably due to a shift in the microbial community toward azide-resistant 1,4-dioxane degrading microbes (e.g., fungi). This study demonstrated for the first time the resilience of the 1,4-dioxane-degrading microorganisms during antibiotic shocks, and the selective enrichment of efficient 1,4-dioxane-degrading microbes after azide poisoning. Our observation could provide insights into designing better 1,4-dioxane remediation strategies in the future.

Characterization of 1,4-dioxane degrading microbial community enriched from uncontaminated soil

1,4-Dioxane is a contaminant of emerging concern that has been commonly detected in groundwater. In this study, a stable and robust 1,4-dioxane degrading enrichment culture was obtained from uncontaminated soil. The enrichment was capable to metabolically degrade 1,4-dioxane at both high (100 mg L^-1) and environmentally relevant concentrations (300 μg L^-1), with a maximum specific 1,4-dioxane degradation rate (q_max) of 0.044 ± 0.001 mg dioxane h^-1 mg protein^-1, and 1,4-dioxane half-velocity constant (K_s) of 25 ± 1.6 mg L^-1. The microbial community structure analysis suggested Pseudonocardia species, which utilize the dioxane monooxygenase for metabolic 1,4-dioxane biodegradation, were the main functional species for 1,4-dioxane degradation. The enrichment culture can adapt to both acidic (pH 5.5) and alkaline (pH 8) conditions and can recover degradation from low temperature (10°C) and anoxic (DO < 0.5 mg L^-1) conditions. 1,4-Dioxane degradation of the enrichment culture was reversibly inhibited by TCE with concentrations higher than 5 mg L^-1 and was completely inhibited by the presence of 1,1-DCE as low as 1 mg L^-1. Collectively, these results demonstrated indigenous stable and robust 1,4-dioxane degrading enrichment culture can be obtained from uncontaminated sources and can be a potential candidate for 1,4-dioxane bioaugmentation at environmentally relevant conditions. KEY POINTS: •1,4-Dioxane degrading enrichment was obtained from uncontaminated soil. • The enrichment culture could degrade 1,4-dioxane to below 10 μg L^-1. •Low K_s and low cell yield of the enrichment benefit its application in bioremediation.

Bioaugmenting the poplar rhizosphere to enhance treatment of 1,4-dioxane

1,4-Dioxane is a highly mobile and persistent groundwater pollutant that often forms large dilute plumes. Because of this, utilizing aggressive pump-and-treat and ex-situ technologies such as advanced oxidation can be prohibitively expensive. In this study, we bioaugmented the poplar rhizosphere with dioxane-degrading bacteria Mycobacterium dioxanotrophicus PH-06 or Pseudonocardia dioxanivorans CB1190 to enhance treatment of 1,4-dioxane in bench-scale experiments. All treatments tested removed 10 mg/L dioxane to near health advisory levels (<4 μg/L). However, PH-06-bioaugmented poplar significantly outperformed all other treatments, reaching <4 μg/L in only 13 days. Growth curve experiments confirmed that PH-06 could not utilize root extract as an auxiliary carbon source for growth. Despite this limitation, our findings suggest that PH-06 is a strong bioaugmentation candidate to enhance the treatment of dioxane by phytoremediation. In addition, we confirmed that CB1190 could utilize both 1,4-dioxane and root extract as substrates. Finally, we demonstrated the large-scale production of these two strains for use in the field. Overall, this study shows that combining phytoremediation and bioaugmentation is an attractive strategy to treat dioxane-contaminated groundwater to low risk-based concentrations (~1 μg/L).